Synthesis of semiconductor nanoclusters

1
Synthesis of semiconductor nanoclusters

• Synthesis of semiconductor nanoclusters
• ???????
• ??????? ?????
• ??? ???? ?? ??(???)
• ? ? ?

2
Semiconductor nanoclusters ?? -??,??? bulk
????? semiconductor nanoclusters ?
short-range structure - bulk?? ?? ??? ? ?? Free
energy ?? ???? ??? ?? -??? ??? ?? ??
? quantum size effects, photocatalysis,
nonlinear optical properties, photoconductivity
3
semiconductor cluster ??? ?? ??
semiconductor cluster? ?? ?? ?? ?? ??
???? ?? ?? 1. ?????? semiconductor cluster
??? ?? data? ?? ???? ??. 2.?????
??(reduciblity) ?? ??(oxidizability)? ???. EX)
I3-?? ? ?? ????? BiI3 cluster ????? ???
??size-quantization? assign ??. Z-?? ??? ??
??? BiI3????? ??? ??? ??? ??, ???,53(2),261
(1995)
4
cluster size random?? amorphous ?? ????
crystalline semiconductor? ???? ??? ?? cluster?
size cluster? size powder X-ray diffraction
data? identity, phase
?? ?? ??.
5

• EX) . PbS cluster
• PbS cluster? phase? size computer? diffraction
  pattern? ???
• ??? ??.
• Scherrer equation? ?? diffraction peak? width?
  ?? cluster
• size? ? ? ??. ( Scherrer equation L
  0.94?/H cos?)
• - computer? simulate? ?? ???? Scherrer equation?
  ? ?? ?? ??.

6
(No Transcript)
7
cluster absorption coefficients? ??
absorption spectrum???? band gap energy? ??
????absorption coefficients? ??? ?.
a 2.304 (OD)/ d (OD)
ad /2.304 absorption spectrum? ??? Data?
?? chemical analysis? ??? cluster? ????? ??? ? ?
??. I Io exp(- ad)
8

• EXAFS (extended X-ray absorption fine
  structure)??
• cluster? local structure? ???? ??? ??
• X-ray powder diffraction data? Mn? location? ??
• ??? ZnxMn1-xS? ?? 3???? ???
• ?? ??? ??.
• -????? ??? chemical identity? atom?
• coordination number? ? ? ?? ?? ???
• ??? local band lengths? ??.

9
?? cluster size?? colloid? ??? ?? ?? cluster
size?? ? particle?? ??? ?? ?? ? cluster? ???
??(colloid? ???) agent? ??. agent agent,
Capping agent, Capping ligand ( ?? ??,
??? ??)
10
? solvent ??? small cluster? stabilizer? ???? ?.
(Zn? ??? ?? ????? ???? alcohol?? ZnO? ??? ?? ??)
0 ? ???? ?? colloids? ??? bulk material? ????
?? design? ??? ???? polymeric surfactant(????)/sta
bilizer? ??. (polymer? ?? electrostatic?? ???
? cluster? ??? ?? ? ??? ??? ???.) 0 ?? ??
???? polymer sodium polyphospate?? CdS, CdTe,
ZnFe? ??.
11
? ??? ?? approach? ???? cluster? ??? ????
capping agent? ???? ??. 0 ???? ???? ?
agent? semiconductor ????? ???? cluster? ??? ????
cluster? ??? ????? ?????? ? ??? ??? ???. 0
Thiophenolates? ?? ????? ???? capping agent
12
(No Transcript)
13
? ??? ???? cadmium? sulfide ion? ??? ????. 0
CdS cluster? ??? propagation step ???? cadmium?
sulfide ion? ??? ??? ? ??? ?. 0 cluster?
??? Thiophenolate ion?? capping agent? ?????? ??
?? ??? ???? (? ??? cluster surface? ??????
growing cluster? intercept??). 0 Cluster size?
?? Solution?? sulfide? Thiophenolate? ???
?????? ?? ? CdSe ? capping agent capping
agent ???????????(TOPO)
Bawendi (1993)
14
??? ? Cluster(Charge cluster)? ??? ?? Cluster?
?? ??? charge transfer??? ?? Cluster? ???
??? 0 charge transfer?? ?? ??(Fe) Cluster?
??? ???? charge? ?? Electical double layer?
??? ???, ?????? ??? 0 charge transfer?? ??
??(Si) Cluster? ??? ????? charge? ?? ???
????, ?? ????
15
??? ? ??? ?? ?? cluster ?? ?? ??? ? ??? ??
cluster? ?? ??? ?? ? EX) Cu? ?? ? ?? ()
Charge ?? cluster? ?? ??? ?? (-) Charge ??
cluster? ?? ??? ???
16
??? ?? Cluster? charge ?? ?? ?????
????? charge ?? 0 ?? charge? ? ???
???? ???? ?? Cluster? Oxide??? ??
???? 0 ?? charge? ? ??? ??? ???? ??
Cluster? Oxide??? ?? ????? ??
?? ??? ? ??
17
Cluster? ???? charge? ?? ?? ?? 1.Cluster?
Ionization energy ?? ?? 2.Surface? Work function?
?? ?? ??????? ??? Cluster? ()Charge?
?? ?
18
Cluster? ?? Force ?? Cluster? ?? Force?
?? Cluster?? 0 ?? Cluster? ????? ?? ???
???? 0 ?? Cluster? ????? ? ??? ???? EX)
Rod-shape ? Cluster? ??? ?? ???? ??? ?? 1?? ??
???? ???? ?? Nanowire? ??.
19
Semiconductor nanoclusters ?? ?? 1.
Top-down approach BulK ?nanocluster EX)
Lithography, Ball milling 2.Bottom-up approach
Atom,Molecular ?nanocluster
EX) Colloidal Synthesis ( ???, ????...)
20
Semiconductor nanoclusters ??? ??
?? BulK?? semiconductor ???(MP),???(BP), ??,
?????, ????? ?? ?? ????? ?? Nanocluster??
semiconductor Size? ?? ????? ????? ??? ????
??
21
Semiconductor nanoclusters ??? ?? ??
Nanocrystal - 3 D Quantum
layer - 2 D Quantum wire - 1 D
Quantum dot - 0 D 1.???? ??? ??? ???
2. ??????? ???
22
(No Transcript)
23
(No Transcript)
24
EX) Quantum dot ??? ?? ??? ?? ?? ZnSe? Size
??? 1.2 ?? 12nm ? ?? ?? Band Gap?? ? 3.4?? 2.7
eV ??? ???.(Bluk 2.8 eV)
Bawendi (1993)
25
Quantum Size Effect 0 ?? ?? R.C.Jaklevik,
Phys.Rev B, (1995) , Au,Ag, Pb,
Mg ??? 0 Energy Band ?? 0 ??? Spectra?? 0 ????
?? 0 ???(Photoefficient) 0 ??-?? ?? ??
(TiO2...) 0 ??? ?? ?? Co??? ??
10-100nm ???? ???)
26
Quantum Size Effect -???- 0 ? ???? ????
??? ?? ? ???? ???? ?? 0 ??? ??(Photochronic )


27
??? ? ??? ???? ???? ??? ?? ? ???? ????
??? Bottom-up-approach Atom, Molecular
?nanocluster EX) Colloidal Synthesis
Chemical Bath Deposition Process? ??
28
Chemical Bath Deposition Process N.R.Pavakar,
J.Electrochem. Soc Solid-State
Sci.Tec.124(5),743(1978) 1. CdSo4 4(NH3)
?Cd(NH3)4SO4 2. Diffusion of the complexion,
OH-, and the catalytic of CdS 3.
H2NNH2CS OH- ?CH2N2 H2O HS- 4.
Formation of bivalent sulfide ions
Hs- OH- ?S2- H2O 5. Formation of CdS
Cd(NH3)42 ?CdS 4NH3
29
???? (1)Z-?? ??? ?? ??? BiI3????? ??? ??? ???
??, ???,53(2),261 (1995) (2) capping agent
???????????(TOPO)
Bawendi (1993) (3) ZnSe? Size ??? 1.2 ?? 12nm ?
?? ?? Band Gap??? 3.4?? 2.7 eV ??? ???.(Bluk
2.8 eV)
Bawendi (1993) (4) R.C.Jaklevik,
Phys.Rev B, (1995) (5) N.R.Pavakar,
J.Electrochem. Soc Solid-State
Sci.Tec.124(5),743(1978)